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Comments on Is this a known design pattern: a piece of code is responsible for acting as a central proxy for data distributed in various places?

Post

Is this a known design pattern: a piece of code is responsible for acting as a central proxy for data distributed in various places?

+3
−1

I have several classes (C_1...C_n) and their instances (I_1....I_m). I have a "Registry" R of these.

There are several pieces of data (d_1...d_k) spread across various instances. This much is set in stone, i.e. I consider the data being spread across the instances as appropriate design.

class Server { // C1
  public String host; // d_i
  public String port;
  //....
}

class Administrator { // C2
  public String username; // d_j
  public String hashed_password;
  public Server belongs_to;
  //....
}

// ....

class SomethingElse { // Cn
   // more of this later
}

class RegistryOfWellKnownInstances {
   getServers(); // I_j
   getAdministrators(); // I_k
   // ...
}

Now while writing the code in C_i, each class does know how to access the data that it's responsible for (among the d_j), but I wouldn't like it to have that knowledge for the data in other classes / instances.


/**
 * Let's say there's a concept of certain well-known instances with the Registry. There are servers "testing" and "prod" and we want access to the host name (d_i) and admin usernames (d_j) for them.
 * This class doesn't have too much knowledge about the `Server` class or `Administrator` class. They are complex classes, and perhaps managed by another set of programers. It doesn't even care about how/where these instances are created and how it'll have access to those instances.
 */ 
class SomethingElse {
  // ...
}

I'm thinking of achieving this by declaring a singleton class X which has access to this registry, and it acts as a proxy between the actual location of the data (in I_j) and the name of the data d_k.

// I could directly encode logic for getting the data from the registry in the class "SomethingElse", but it's actually needed by others as well, so let's define something common

class X {
   // NOTE: I'm aware that I can parametrize this with "prod" or "testing" but for sake of example let's say these are simple getters without a parameter.
   // These methods would work by essentially getting instance from registry and just invoking appropriate getters / accessing appropriate fields 
   get_prod_hostname() // d1
   get_testing_hostname() // d2
   get_prod_admins()  // d3
   get_testing_admins()  // d4
   // ....
} 

So using X, anywhere in my program I can write X.get_d2() and I'll get d2, without worrying about where it came from.

Is this a known design pattern? If not, then are there any obvious pitfalls with this design that some other patterns are known to mitigate?

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1 comment thread

General comments (10 comments)
General comments
Alexei‭ wrote almost 3 years ago

This is an interesting question. I am thinking of something like Redux which deals with state management. It would be useful if you can provide a simple example like 3 classes with 3 data types to understand the nature of your application (e.g. is the data related to the state or is it something else?).

elgonzo‭ wrote almost 3 years ago · edited almost 3 years ago

Unless i am mistaken, your X sounds like an implementation of the Facade pattern (https://en.wikipedia.org/wiki/Facade_pattern). But, i am not entirely sure whether your question is specifically about X or about some other aspect of your code structure and logic, though...

peey‭ wrote almost 3 years ago

I'll add an example so that things are clearer.

peey‭ wrote almost 3 years ago

@Alexei that's a useful comparison. I think redux but without centralizing everything, and just centralizing a subset of data is a useful comparison. In my real scenario the data is related to state, but I've tried to generalize it in the question.

peey‭ wrote almost 3 years ago

@elgonzo I'm also feeling similarities with Facade, but I am not completely sure due to it not being a facade on classes but on some well-known instances. Perhaps what I have here is a weird mix of 2 design patterns which is becoming the root cause of the confusion.

elgonzo‭ wrote almost 3 years ago · edited almost 3 years ago

Hmm, you said you have instances of C_1 ... C_n classes. Why is it then not about classes? The facade pattern is about "hiding" the structure and complexities of a (sub)system and present (some of) its functionality through a simplified interface (the facade, in your case X). Your comment leaves me even more confused :(

Skipping 2 deleted comments.

elgonzo‭ wrote almost 3 years ago

If it is about having different "SomethingElse" instances with their individual incarnations of C_1 ... C_n instances, well, I don't know nothing about this "SomethingElse" except its name and that you call it a "registry" of C_1 ... C_n instances. So, again i can't tell with certainty, but from the little i know "SomethingElse" sounds like being just a composite datatype (as in "object composition"; which is not a design pattern and should not be confused with the composite design pattern)...

peey‭ wrote almost 3 years ago

@elgonzo because it's about the two particular instances ("testing" server and "prod" server in the example). There may be other instances which X doesn't care about, and neither does SomethingElse

Alexei‭ wrote almost 3 years ago

X class (instance) seems like a God object to me. Why do you need to centralize so much heterogenous functionality in one place?

Lundin‭ wrote almost 3 years ago

You simply can't discuss proper program design in vague and abstract terms - that's nothing but a source of pointless & badly designed abstraction layers. What is the data that's being passed around and why does it need to be passed around? Does each node know the destination or is it the server object's responsibility to find out? How? Are there addresses? Are the nodes in physical different locations (clients, bus nodes etc) or in different processes, or in the same process? And so on.